1. Field of the Invention
The present invention relates to an erbium-doped fiber amplifier using erbium as an amplification medium, and more particularly to a dispersion-compensated erbium-doped fiber amplifier using a dispersion-compensated optical fiber.
2. Description of the Related Art
In response to the greatly increased amount of data being transmitted, recently-developed wavelength division multiplexing (WDM) optical communication systems have increased their transmission capacities. Such an increase in transmission capacity can be achieved by increasing the number of transmission channels, or, by increasing the rate of data transmission. Currently, increasing the rate of data transmission is the method of choice and can provide a data transmission rate increased from 2.5 Gb/s up to 10 Gb/s. In order to realize a higher data transmission rate, a number of research efforts are ongoing.
Dispersion effects are severely increased at a transmission rate of 10 Gb/s or more. Accordingly, dispersion compensating fibers are used in order to compensate for the dispersion that occurs during a transmission procedure. However, where such a dispersion compensating fiber is used, it is also necessary to additionally use an optical fiber amplifier in order to compensate for the accompanying additional loss of optical signal power.
FIG. 1 illustrates a prior art dispersion-compensated erbium-doped fiber amplifier 10. As shown in FIG. 1, the prior art dispersion-compensated erbium-doped fiber amplifier 10 has a dispersion compensating configuration including a first and second erbium-doped fiber 110 and 112, connected to each other in series, and a first and second dispersion compensating fiber 130 and 132 arranged between the first and second erbium-doped fibers 110 and 112, and connected to the first and second erbium-doped fibers 110 and 112 in series while being connected to each other in series. The fiber amplifier 10 supplies a first pumping light to the first erbium-doped fiber 110 in a forward fashion via a first wavelength selective coupler 118, while supplying a second pumping light to the second erbium-doped fiber 112 in a forward fashion via a second wavelength selective coupler 120, in order to amplify optical signals flowing through the fibers 110 and 112. When a pumping light is supplied to the first or second erbium-doped fiber 110 or 112, the erbium ions maintained in a ground state in the fiber are excited by the pumping light. As the excited erbium ions are induced to be emitted in accordance with an inversion thereof, optical signals are subjected to an amplification procedure while passing through the fiber. During the amplification procedure, an amplified spontaneous emission (ASE) is generated. First through fourth isolators 122, 124, 126 and 128 are provided to cut off backward flowing of the ASE while allowing the amplified optical signal to flow forward.
In WDM communication systems using a transmission rate of 10 Gb/s or more, however, it is necessary to use a dispersion compensating fiber for dispersion compensation, and a fiber amplifier for compensating for loss of optical signals caused by the use of the dispersion compensating fiber. Where the number of nodes in a network having a ring architecture is increased, or the transmission distance in a long-distance transmission system is increased, the numbers of dispersion compensating fibers and dispersion compensating fiber amplifiers required in the transmission system are correspondingly increased. When the number of components increases the cost of manufacturing is also increased whereas the reliability of the system decreases.